With the current desire for fuel efficient and low emission vehicles, many novel solutions for internal combustion engine architecture and operating strategy have been developed. One such idea is the Belt Alternator Starter (BAS) hybrid propulsion system. This system provides increased fuel economy by shutting off the engine when at an idle operating mode, or idle stop, and enabling early fuel cut-off during decelerations. The BAS hybrid propulsion system can also accommodate regenerative braking. The hybrid propulsion system combines engine controls with a combined alternator/starter motor, or motor/generator. This hybrid strategy has minimal impact on engine and transmission architectures when compared to other hybrid strategies.
A typical automotive accessory drive system consists of a drive pulley connected to an output shaft of the engine, usually the crankshaft. Wrapped around this pulley is a flexible drive belt, which in turn is wrapped around a plurality of driven pulleys. This flexible drive belt transmits drive forces between the drive pulley and the driven pulleys. The driven pulleys may be fixably attached to accessories known in the art, such as a power steering pump, air conditioning compressor, alternator, and secondary air pump. However, some of these driven pulleys may be idler pulleys which may be used to ensure proper belt wrap of a given driven pulley or they may be used to ensure proper belt routing.
The hybrid propulsion system employs a motor/generator mounted with respect to the other components of the accessory drive system. The motor/generator can be mounted in effectively the same way and in effectively the same packaging space as a traditional alternator. The hybrid propulsion system must be able to effect a quick restart of the engine.
When a request is made to restart the engine, usually by depressing the accelerator pedal or releasing the brake pedal, the driven pulley mounted to the motor/generator will impart, to the output shaft, the rotational force necessary to rotate or “crank” the engine via the flexible drive belt. Traditional hybrid propulsion systems employ an auxiliary transmission oil pump to maintain fluid pressure within the transmission during the idle stop mode of operation. This is necessary to ensure that the torque transmitting mechanisms remain engaged when the mechanical oil pump operation is discontinued upon engine shut down.